A gas hydrate is ice-like solid crystals formed of water molecules and gas molecules, and is a generic term referring to clathrate hydrates (hydrates) in each of which each gas molecule is included inside a cage constructed of water molecules with a three-dimensional structure. The gas hydrate has been actively studied and developed as transportation and storage means for natural gases because the gas hydrate contains a natural gas in an amount as large as approximately 165 Nm3 per 1 m3 of the gas hydrate.
As apparatuses for producing gas hydrates, there have conventionally been the following systems: a bubbling system (see, for example, Japanese patent application Kokai publication No. 2003-80056) in which a raw-material gas is blown into a raw-material water in a generator; a spray system (see, for example, Japanese patent application Kokai publication No. 2002-38171) in which a raw-material water is sprayed into a generator filled with a raw-material gas; a tubular reactor system (see, for example, Japanese patent application Kokai publication No. 2002-356685) using a line mixer and a water-tube-type tubular reactor; and the like.
However, the bubbling system has the following problems and the like because the bubbling system includes: a generator with an agitator; an external cooler that removes a generated heat (called also a reaction heat); a gravity dehydrator (called also a gravity dehydrating tower) in which a gas hydrate slurry, generated by the generator and then introduced thereinto, is dehydrated by utilizing gravity so that an unreacted water is removed therefrom. Specifically, (1) the bubbling system requires the agitator, (2) the bubbling system requires two devices, that is, the generator and the external cooler, (3) the dehydrator is large in size because of the gravity dehydration, and (4) the dehydrator is difficult to control because of the gravity dehydration.
Meanwhile, the spray system has the following problems and the like because water is sprayed from a nozzle into the generator filled with a raw-material gas. Specifically, (1) the speed of producing a gas hydrate is slow, and (2) the cooling of a raw-material gas in the generator with the external cooler is associated with a poor heat transmission.
On the other hand, the tube system has the following problems and the like. Specifically, (1) the tubular reactor is long, and (2) a pressure drop is large because of the long tubular reactor.